DE4324066A1 - Screening device - Google Patents

Abstract

PCT No. PCT/EP94/01393 Sec. 371 Date Jan. 17, 1996 Sec. 102(e) Date Jan. 17, 1996 PCT Filed May 2, 1994 PCT Pub. No. WO95/02466 PCT Pub. Date Jan. 26, 1995Described is a screening device (1) with a screen fabric (2) having two groups of threads, the threads of one group running substantially orthagonal to the threads of the other group. A screening device of this kind can be more easily monitored to detect breaks in the screen fabric. For this purpose, electrically or optically conductive threads are provided in the second group at a predetermined lateral distance from one another. The threads of the second group are mechanically supported by the threads of the first group and are insulated relative to one another at least in some portions electrically or optically with respect to the physical quantity. An input arrangement and output arrangement (6, 7) is provided, respectively, at two edges of the screen fabric (2) which extend substantially parallel to the threads of the first group, this input arrangement and output arrangement (6, 7) being connected at least with the conductive threads of the second group in a conducting manner.

Description

The invention relates to a screening device with a Screen fabric, which has two groups of threads, wherein the threads of one group are essentially orthogonal to the threads of the other group.

Sieving devices, in the following also called sieves are used in a variety of applications to sort out particles from a product that do not exceed a certain size. Such Sieves are also used, among other things, to cut off to obtain gear product that is free of foreign bodies is. A particularly important area of application is found themselves in the food industry and in pharmazeu table industry. Products that are for the human consumption are meant to be prepared. For example, flour has to be sieved so that it is free of foreign bodies, like stones. When grinding nuts Care must be taken to ensure that there are none in the end product Nutshells are included. Such stones or Nutshells can damage teeth in the consumer cause.  

The sieve fabric is subject to relatively high stress, among other things, through vibrations that arise hen that the material to be screened moves over the screen cloth becomes. Without such a movement, however, one is satisfied the practicing sieving practically cannot be ensured. The stresses can lead to damage of the screen mesh. The screen mesh then gets one Hole that is larger than the mesh size, so that too Particles with a size to be separated in and of themselves ß get into the starting product. Even if the Failure to notice is usually a relatively large one large amount of the starting product is treated again, to make sure that since the occurrence of the error not accidentally a disturbing foreign body in the starting product has arrived. Since this is very expensive is lig and for the operator also with a relative the Siebge webe exchanged from time to time. The intervals who which is chosen so that with a very large truth Probably no defect has yet occurred in the screen mesh is. As a result, the intervals must be very short. Many screen fabrics will change at the time of replacement still be completely intact so that the early defrost is basically a waste of material. Except which is usually the replacement of the screen cloth relatively labor intensive because the screening device at least at least partially dismantled. On the other hand, read However, not all mistakes are made up with certainty shut down.

It has various plans in the past given the sieve mesh with tools monitor. DE 24 43 548 A1 is a device to control the wear of technically stressed Known panels of fabric in which to be checked Fabric web at least one electrically conductive control thread is inserted at intervals to determine  his cross that goes hand in hand with wear cut acceptance with a measuring device for determination associated with the increase in its electrical resistance is. Here, however, there is the problem that in the A control thread is also inserted into the fabric. This control thread locally changes the mobility of the Screen mesh. It gets tough around the control thread ter. This also affects the vibration behavior of the sieve tissue changes, leading to an increased risk Screen fabric in the neighborhood susceptible to breakage of the control thread. You can also use a such control thread only a relatively rough over monitor the screen mesh. Damage, which are within the size of a few stitches holds, can usually not be recorded.

DE 31 43 779 A1 shows a device on visual or Screening devices for monitoring viewing or screening cloths for crushing and sorting plants of the Hütten- und Steinin industry, in which areas of the cloth between the View or sieve holes in a line loop in or is attached to the cloth, which is connected to an electrical Lei is connected to a circuit electrically operated control, registration or Alarm device is connected. If the line loop is interrupted or short-circuited this is an indication that the cloth is in one place is damaged. This damage is said to be electrical summarized and displayed. Here again results the problem that the damage is not reliable enough can be grasped. In particular, the case occur that the cable loop comes loose from the cloth, which does not necessarily have to be noticed, so that a subsequent damage to the cloth is not detected can be.  

Furthermore, it is known from DE 16 48 368 A1, one under a certain angle of incidence on the abrasion surface of the screen fabric falling and reflecting portion to measure a radiation which changes with the change of the Abrasion also changes. When you reach the top too The degree of abrasion of the sieve fabric becomes a signal triggered. This process is said to be in the paper industry be used in which the paper screens are made of wires are formed, the corresponding Reflexionsver have to hold.

The invention has for its object a sieve to specify the direction that error monitoring with ho her reliability.

This task is the one with a screening device gangs mentioned solved in that in the second Group in predetermined lateral distances are seen, which guide for a physical quantity are that the threads of the second group through the Threads of the first group mechanically supported and closed at least in sections for the physical quantity are isolated from each other and that at two essentially lichen parallel to the threads of the first group edges of the screen fabric each one on or off Feed arrangement is provided, at least with the conductive threads of the second group for on or off supply of the physical quantity is connected.

In particular, the physical quantity is electrical Electricity into consideration, but also other flowing media, Light, sound, pressure can be considered physical quantities be used. The formation of the threads of the second Group depends on the one to be transferred, i.e. H. to senior size. In the case of electricity, an electri cal conductivity required, with light a light conductivity. When directing flowing media,  especially gases, a corresponding channel must be pre-selected to be seen. Pressures can either correspond to one channel through the threads or, if the pressures are negative, i.e. as tensile forces forms, act directly on the threads. The one For the sake of simplicity, the invention is described below described by electrically conductive threads, the Entry and exit arrangement as electrodes order is formed. The invention aims at this but not be limited. When using other physical properties is the property "elek trisch "by the necessary property for the corresponding appropriate physical quantity to replace. The same applies to the term "electrode arrangement". In Ge contrast to the previously known facilities the error monitoring here no longer indirectly additional aids that are inserted into the screen mesh be brought, but directly through the screen mesh itself. The vibration behavior of the Sieve mesh through additional control threads or lei tion loops not negatively affected. The sieve rather, tissue can be made relatively homogeneous the, so that additional burdens from "Störstel len ", which results from the vibration of the screen fabric ben can be avoided. Surveillance is also more reliable in that the aids are not can remove more of the screen mesh. The for monitoring Rather, the means used are more integral and essential part of the sieve for the sieve function fabric. The permissible fault tolerance can be determined by the lateral distance between the electrically conductive threads second group. If a hole in the Screen fabric is created, becomes a thread of the second group damaged. This can be displayed immediately. There the threads of the second group through the threads of the first Group not only mechanically supported, but also at least in sections electrically iso against each other  are liert, can be relatively simple with electri means of good error monitoring, because the break of an electrically conductive thread of the two group made a clear resistance resistance tion that can be detected to trigger an alarm to solve.

All threads are preferably of the second group electrically conductive. This allows on the one hand make sure that even the smallest defects in the sieve weave can be grasped. On the other hand, here by also implementing a tiered error monitoring. In many cases it is harmless if only one thread tears because the resulting sieve opening is still is small enough to prevent foreign objects from passing through allow. In such a case one is ge warns that there is damage because the electrical resistance of the mesh has changed, an exchange of the screen mesh is not yet necessary. This can be done at the next opportunity, e.g. B. with regular maintenance, vorgenom men. Only when a second thread breaks does it have to Screen fabric to be replaced. This can be given if necessary, refine it so that it is determined which thread is broken so that an exchange of the Sieve cloth must only be made immediately, when two threads lying next to each other are torn.

The threads of the first group are preferably in the form of a warp threads and the threads of the second group as weft threads educated. The warp threads usually have a high here firmness than the wefts. Now if the shot threads are used for error monitoring, the weaker link monitored, in which an error with large more likely to occur. The reliable This will further improve error monitoring increases.  

The screen fabric is preferably a synthetic fiber fabric formed, threads of the second group of fibers an electrically conductive plastic in at least have an electrically conductive connection. Synthetic fiber fabrics have the necessary elasticity and Vibration ability. Fibers from an electrical conductive plastic, especially carbon fibers, ha in many cases have similar properties to others Synthetic fibers so that when used one in both Directions of area extension of homogeneous tissue can be aimed at a correspondingly uniform Shows vibration behavior and not on individual sturgeon tends to break. In addition, the vibration resilience of carbon fibers many times higher than that of metal wires. Single metal wires ver in many cases become brittle under a vibration layer so that they break easily. In this case the ability to monitor the tissue prematurely against wear.

It is very particularly preferred that the synthetic fiber is formed by polyester, the threads of the two group of polyester with carbon or only carbon are formed. Such a compilation has Proven as screen mesh.

The threads of the second group are preferably each because to bundle at least two individual threads together amount, with at least one thread of a bundle is electrically conductive. So the threads don't have to be formed as individual threads. You can too several can be summarized, one each Bundle of threads between individual sieve holes or -Ma is arranged. This allows on the one hand the mechanical stability of the thread bundle relative regardless of the mechanical stability of an elec Select tric conductive thread. On the other hand, the  Homogeneity of the sieve not disturbed. The fail-safe Unit is not affected by the bundle of threads. As long as at least one thread of the bundle is still intact sieve function is fully maintained Only when all threads of a bundle are torn the sieve function is no longer guaranteed to be error-free continuous In this case, the electrically conductive is also capable thread broken.

It is preferred that the product to be screened is a Main direction of movement relative to the screen mesh in the we substantially perpendicular to the threads of the second group has, wherein the at least one electrically conductive thread of the bundle of threads in the main direction of movement behind an electrically non-conductive and mecha nisch stronger thread of the bundle is arranged. Of the electrically conductive thread is, so to speak, in the "Slipstream" of the mechanically stronger and electric not necessarily conductive thread. This also leaves the mechanical resilience of the sieve mesh re relatively independent of the mechanical resilience choose a single, electrically conductive thread. However, the reliability is not affected. In most cases, mechanical becomes the first stronger thread and exposed to the material pressure eat. As long as the electrical thread is still intact the sieve function undisturbed. The electrically conductive However, thread will soon break and a mistake Generate message.

The electrode arrangements advantageously switch the threads of the second group are electrically parallel. The Electrode arrangement can thus be a relatively simple one Have structure. The electrical wiring is also there through relatively simple.  

It is also preferred that the electrode arrangements Mechanically support the screen mesh. The electrode arrangement This means that not only has the task of ensure wiring of the sieve cloth, they also take over the mechanical support. Hereby the support can also be checked so that also damage to the support of the screen fabric, which also leads to contamination of the exit product could lead, can be detected.

Preferably, the electrode arrangements are over each an electrically insulating support on a frame supported. The screen fabric is thus opposite to the Screening device electrically insulated. Any Protective measures no longer have to be taken.

Preferably at least one is attached to the electrodes order effective and the screen mesh exciting stand holder is provided, which is electrically conductive, electrical at one end with an electrode assembly is connected and at the other end an electrical Has connection, the other electrode arrangement is electrically isolated from the spacer and ei NEN has its own electrical connection. The Ab stand not only ensures the mechanical Tension of the sieve fabric, which is satisfactory for one the functioning of the screening device is necessary. He is also the electrical connection through which one Electrode arrangement connected to a measuring device can be on the same side of the Screen fabric like the other electrode arrangement. By this relatively simple measure appears to be the Manageability of the screening device is very considerable improves. The electrical connection for monitoring can done from one side.  

The spacer is preferably on the outlet cable te of the screen fabric arranged. The spacer will so that only the already sieved starting product is used strikes. The risk of damaging the spacer is kept low.

In a particularly advantageous embodiment, this is Screen fabric arranged in the form of a hollow cylinder where in the threads of the second group essentially par allel to the cylinder axis. Here you can the desired relative movement between the screenings and the sieve by rotating the hollow cylinder around it Reach axis. The electrode arrangements are located then advantageously on the end faces of the Hollow cylinder, so that the entire length of the mesh is monitored.

It is preferred that the electrode arrangements are designed as stainless steel rings. The stainless steel rings also serve as a support for the screen mesh, so that it is held in the desired cylindrical shape becomes. Stainless steel rings have sufficient electri conductivity. On the other hand, they are mechanical sufficiently resistant to wear from the product to be screened.

Preferably the screen fabric is essentially plan between the two electrode arrangements is tense. In this case, the screen mesh forms Plansieb.

A resistance measuring device is preferably provided see that with both electrode assemblies electrically connected and with an increase in electrical Resistance between the two electrode arrangements generates an alarm signal. The simple measurement of the Wi  this is enough to make a mistake on the part of the sieve to capture webes. The same applies to other phy sical sizes. Here then the portability must the respective size can be determined.

It is also preferred that the resistance measurement direction contains a differentiator that the Zeitli che change in resistance is determined, whereby it Alarm signal triggers when the resistance change per Unit of time exceeds a predetermined amount. Hereby can avoid a number of false alarms that for example, could occur if the contra status change not caused by damage to a company dens, but for example by changing the Ambient temperature is effected. Such a change tion is usually relatively slow, while the Change in resistance due to the breakage of a thread rela tiv suddenly occurs. This also increases the confidence casualness of the screening device increased.

The invention is preferred below on the basis of one th embodiment in connection with the drawing described. Show here:

Fig. 1 shows a screening device schematically in cross-section,

Fig. 2 is a screen fabric in plan view,

Fig. 3 is an enlarged section of Fig. 1 and

Fig. 4 shows an electrical circuit arrangement.

A sieve device 1 has a sieve fabric 2 which has the shape of the outer surface of a hollow cylinder.

The screen fabric has threads 3 of a first group, which are shown in broken lines in FIG. 2, and threads of a second group 4 , which are shown in FIG. 2 by solid lines. The threads 3 of the first group form the warp threads and the threads 4 of the second group form the weft threads of the screen fabric 2 . They limit sieve openings 5 , the size of which are adapted to the size of the particles of a starting product of a product to be sieved.

The threads 3 of the first group are formed by synthetic fibers, for example polyester. The threads 4 of the second group contain carbon fibers in an electrically conductive context, ie they can be formed by polyester with carbon or consist only of carbon fibers. The threads 4 of the second group, which contain the carbon fibers, are thus electrically conductive. As shown in Fig. 2, all threads 4 of the second group can be electrically conductive. But it is also possible to make only every second or third or even every nth thread conductive, as long as it is ensured that in the event of a thread break between the electrically conductive threads 4 of the second group, no opening is formed which is larger than that maximum permissible particle size in the starting product.

The structure of the threads of the first group 3 made of polyester and the threads 4 of the second group made of polyester with carbon or carbon fibers ensure a relatively homogeneous structure of the screen fabric 2 .

The threads 4 of the second group can also be combined in bundles between individual NEN meshes, so that not only a single thread, but a plurality of threads lie between individual meshes, which are either twisted or simply simply arranged in parallel to one another. It is sufficient if a single thread is electrically conductive in such a bundle of fibers.

Parallel to the threads 3 of the first group, two electrode arrangements 6 , 7 are arranged on the longitudinal edges of the fabric 2 . The electrode arrangements 6 , 7 switched the threads 4 of the second group electrically in parallel. The electrode arrangements have the shape of stainless steel rings, on the circumference of which the screen fabric 2 rests. It is (see Fig. 3) festge clamped here by a clamping ring 8 , so that a reliable electrical contact between the electrically conductive threads 4 of the second group and the electrode arrangements 6 , 7 is ensured. Each electrode assembly 6, 7, between the clamping ring 8 and the intermediate space between the two electrode assemblies 6, 7 a bead 9, the withdrawal of the with the clamping ring 8 of procedure on the electrodes at 6, 7 fastened to the screen fabric 2 of the electric end assembly 6, 7 difficult.

Each electrode arrangement 6 , 7 is arranged in an electrically non-conductive plastic ring 10 , 11 . The plastic rings 10 , 11 are in turn rotatably supported in a machine frame 12 , 13 not shown. In many cases, the plastic rings 10 , 11 will also be immovably mounted in the machine frame if a relative movement between the material to be screened and the screen fabric is provided in another way.

The two plastic rings 10 , 11 are held at a predetermined distance from one another by a plurality of spacers 14 , 15 . The spacers, of which more than two can also be provided, are held by support rings 16 . The spacers 14 , 15 ensure that the screen fabric 2 gets the necessary tension in the axial direction of the cylinder.

At one end of the screen drum 17 formed by the screen fabric 2 , in Fig. 1 at the right end, two electrical connections 18 , 19 are provided. One electrical connection 18 is connected via an electrical line 20 running in the plastic ring 11 to the electrical assembly 7 , for example via a steel screw screwed into the plastic ring 11 . The line 20 can be isolated from the spacer 14 .

The electrical connection 19 is electrically connected via a line 21 to the other spacer 15 , which is electrically conductive. The spacer 15 is connected via a further, arranged in the plastic ring 1 electrical line 22 with the other electrode arrangement 6 . The necessary electrical signals can thus be generated or obtained via a single end face of the screening drum 17 , namely from the right end face shown in FIG. 1. For example, can be measured between the two electrical connections 18 , 19, the resistance of the screen fabric 2 in the axial direction. The electrical resistance of the spacer 15 is negligible since it will generally be constant. If necessary, it can be compensated for by suitable electrical means.

The entire screen fabric 2 has an electrical resistance in the axial direction in the range of 500 to 1000 Ω. If only one of the threads 4 of the second group breaks, the electrical resistance increases in the range from 0.25 to 0.5 Ω. This resistance increase can be measured and used as a signal for a broken screen. For example, on the basis of the signal, a display 23 can be actuated or the screening drum 17 can be stopped.

Fig. 4 shows schematically an electrical circuit arrangement for evaluating the resistance signal. For this purpose, an evaluation device 24 is provided, which is connected to the electrical connections 18 , 19 of the screening device 1 . The evaluation device 24 has a resistance measuring device 25 connected to the two connections 18 , 19 . With the resistance measuring device, a comparator 26 is connected, which determines whether or not the resistance value of the screen fabric 2 determined by the resistance measuring device 25 exceeds a predetermined value or not. In the event of an overshoot, the display 23 is actuated. Alternatively or additionally, a differentiating element 27 can also be connected to the output of the resistance measuring device, which in turn is connected to a comparator 28 . The comparator 28 determines whether the change in resistance over time is within a predetermined frame. A change in resistance can be done not only by breaking a thread 4 of the screen fabric 2 , but also by changing the temperature. However, temperature changes are generally slower in time, while the change in resistance due to a thread break occurs very suddenly. If the evaluation device 24 determines that there is a sudden change in resistance, the display device 23 is also actuated. As an alternative to this, the screening device 1 can also be stopped.

A sieve drum 17 is shown . However, the device can also be used for flat screens.

Claims (17)

1. Screening device with a screen fabric which has two groups of threads, the threads of one group being substantially orthogonal to the threads of the other group, characterized in that threads ( 4 ) in the second group at predetermined lateral distances. are provided, which are conductive for a physical quantity, that the threads ( 4 ) of the second group are mechanically supported by the threads ( 3 ) of the first group and at least in sections are insulated from one another for the physical quantity and that two are essentially parallel to one another the threads ( 3 ) of the most group running edges of the screen fabric ( 2 ) each have an input or output arrangement ( 6 , 7 ) is provided, which at least with the conductive threads ( 4 ) of the second group for input and output the physical size is connected. 2. Screening device according to claim 1, characterized in that all threads ( 4 ) of the second group are electrically conductive. 3. Screening device according to claim 1 or 2, characterized in that the threads ( 3 ) of the first group as warp threads and the threads ( 4 ) of the second group are designed as weft threads. 4. Screening device according to one of claims 1 to 3, characterized in that the screen fabric ( 2 ) are designed as synthetic fiber fabric, threads ( 4 ) of the second group having fibers made of an electrically conductive plastic in at least one electrically conductive connection. 5. Screening device according to claim 4, characterized in that the synthetic fiber is gebil det by polyester, the threads ( 4 ) of the second group made of polyester with carbon or only carbon. 6. Screening device according to one of claims 1 to 5, characterized in that the threads ( 4 ) of the two th group are each combined into bundles of at least two individual threads, at least one thread of a bundle being electrically conductive. 7. Sieving device according to claim 6, characterized in that the product to be sieved has a main direction of movement relative to the sieve fabric in wesentli Chen perpendicular to the threads ( 4 ) of the second group, the at least one electrically conductive thread of the bundle of threads in the main direction of movement net is behind an electrically non-conductive and mechanically stronger thread of the bundle. 8. Screening device according to one of claims 1 to 7, characterized in that the electrode arrangements ( 6 , 7 ) connect the threads ( 4 ) of the second group electrically in parallel. 9. Screening device according to one of claims 1 to 8, characterized in that the electrode arrangements ( 6 , 7 ) mechanically support the screen fabric ( 2 ). 10. Screening device according to claim 9, characterized in that the electrode arrangements ( 6 , 7 ) are each supported by an electrically insulating carrier ( 10 , 11 ) on a frame ( 12 , 13 ). 11. Screening device according to one of claims 1 to 10, characterized in that at least one on the electrode arrangements ( 6 , 7 ) and the screen fabric ( 2 ) exciting spacer ( 15 ) is seen before, which is electrically conductive, at one end with an electrode arrangement ( 6 ) is electrically connected and has an electrical connection ( 19 ) at the other end, the other electrode arrangement ( 7 ) being electrically insulated from the spacer ( 15 ) and having its own electrical connection ( 18 ). 12. Screening device according to claim 11, characterized in that the spacer ( 15 ) on the upstream side of the screen fabric ( 2 ) is arranged. 13. Screening device according to one of claims 1 to 12, characterized in that the screen fabric ( 2 ) is arranged in the form of a hollow cylinder ( 17 ), the threads ( 4 ) of the second group running essentially parallel to the cylinder axis. 14. Screening device according to claim 13, characterized in that the electrode arrangements ( 6 , 7 ) are designed as stainless steel rings. 15. Screening device according to one of claims 1 to 14, characterized in that the screen fabric ( 2 ) is stretched substantially flat between the two electrode arrangements ( 6 , 7 ). 16. Screening device according to one of claims 1 to 15, characterized in that a resistance measuring device ( 25 ) is provided which is electrically connected to both electrode arrangements ( 6 , 7 ) and with an increase in electrical resistance between the two electrode arrangements ( 6 , 7 ) generates an alarm signal. 17. Screening device according to claim 16, characterized in that the resistance measuring device ( 25 ) contains a differentiator ( 27 ) which determines the temporal che change of the resistance, wherein it triggers the alarm signal when the resistance change tion per unit time exceeds a predetermined amount .